1. Field of the Invention
The present invention relates to a method of preparing a pigment composition, and more particularly to a composition containing a dianthraquinone pigment and/or a diketopyrrolopyrrole pigment useful as pigments of a color filter used in, e.g., a color liquid crystal display device or a solid-state image sensing device.
2. Description of the Related Art
Conventionally, as a red pigment for a color filer used in, e.g., a color liquid crystal display device or a solid-state image sensing device, a dianthraquinone pigment or a diketopyrrolopyrrole pigment, which is high in brightness, and excellent in resistance to light and heat, has been used. However, pigments higher in brightness have been strongly required. To meet the requirement, the transparency must be improved by further decreasing the primary particle size of the pigment.
To decrease the primary particle size of a pigment, Jpn. Pat. Appln. KOKAI Publication No. 7-13016 discloses wet milling a pigment in the presence of a synthetic resin which is solid at room temperature and insoluble in water. Jpn. Pat. Appln. KOKAI Publication No. 2004-277434 discloses dry milling a pigment with addition of a small amount of an organic solvent which has a crystal growing function. Jpn. Pat. Appln. KOKAI Publication No. 10-245501 discloses wet milling a dianthraquinone pigment in the presence of an anthraquinone derivative. Further, Jpn. Pat. Appln. KOKAI Publication NO. 2001-220520 discloses wet milling a diketopyrrolopyrrole pigment in the presence of a pigment derivative.
However, the dianthraquinone pigments or the diketopyrrolopyrrole pigments obtained by these methods are insufficient in brightness, etc.